14,796 research outputs found
Thrust performance of isolated plug nozzles with two types of 40-spoke noise suppressor at Mach numbers from 0 to 0.45
Plug nozzles with two types of 40-spoke noise suppressor were tested at free-stream Mach numbers from 0 to 0.45 and over a range of nozzle pressure ratios from 1.5 to 4.0. In additon, an unsuppressed plug nozzle and a Supersonic Tunnel Association nozzle were also tested to provide baseline levels of thrust performance. The unsuppressed plug nozzle had an efficiency of 98 percent at an assumed takeoff pressure ratio of 3.0 and at Mach 0.36. At the same condition the suppressor nozzles had efficiencies of approximately 83.5 percent
Thrust performance of isolated 36-chute suppressor plug nozzles with and without ejectors at Mach numbers from 0 to 0.45
Plug nozzles with chute-type noise suppressors were tested with and without ejector shrouds at free-stream Mach numbers from 0 to 0.45 and over a range of nozzle pressure ratios from 2 to 4. A 36-chute suppressor nozzle with an ejector had an efficiency of 94.6 percent at an assumed takeoff pressure ratio of 3.0 and a Mach number of 0.36. This represents only a 3.4 percent performance penalty when compared with the 98 percent efficiency obtained with a previously tested unsuppressed plug nozzle
Thrust performance of isolated, two-dimensional suppressed plug nozzles with and without ejectors at Mach numbers from 0 to 0.45
A series of two-dimensional plug nozzles was tested with and without ejector shrouds at free stream Mach numbers from 0 to 0.45 and over a range of nozzle pressure ratios from 2 to 4. These nozzles were also tested with and without chute noise suppressors. A two-dimensional plug nozzle has an efficiency of 96.1 percent at an assumed takeoff pressure ratio of 3.0 and Mach 0.36. A 12-chute suppressed nozzle with sidewalls has an efficiency of 81.0 percent (15.1 percent below the unsuppressed nozzle)
Scattered Lyman-alpha Radiation Around Sources Before Cosmological Reionization
The spectra of the first galaxies and quasars in the Universe should be
strongly absorbed shortward of their rest-frame Lyman-alpha wavelength by
neutral hydrogen (HI) in the intervening intergalactic medium. However, the
Lyman-alpha line photons emitted by these sources are not eliminated but rather
scatter until they redshift out of resonance and escape due to the Hubble
expansion of the surrounding intergalactic HI. We calculate the resulting
brightness distribution and the spectral shape of the diffuse Lyman-alpha line
emission around high redshift sources, before the intergalactic medium was
reionized. Typically, the Lyman-alpha photons emitted by a source at z=10
scatter over a characteristic angular radius of order 15 arcseconds around the
source and compose a line which is broadened and redshifted by about a thousand
km/s relative to the source. The scattered photons are highly polarized.
Detection of the diffuse Lyman-alpha halos around high redshift sources would
provide a unique tool for probing the neutral intergalactic medium before the
epoch of reionization. On sufficiently large scales where the Hubble flow is
smooth and the gas is neutral, the Lyman-alpha brightness distribution can be
used to determine the cosmological mass densities of baryons and matter.Comment: 21 pages, 5 Postscript figures, accepted by ApJ; figures 1--3
corrected; new section added on the detectability of Lyman alpha halos;
conclusions update
Rationale for tau aggregation inhibitor therapy in Alzheimer's disease and other tauopathies
Preprin
- …